Battery Bank

[Beatenbo]

Hello, A lot of ? about how many or much. I had a 2,000 watt inverter 12V input with 6 T-105 Trojans.  I think they are 225 amp hr. I haven't been to school on eletronics but some times this is confusing.  I know with AC volts Vots devided into wattage will give you amp. But this DC thing is sometime hard to figure.   My almost new 2,000 watt inverter went out. In the mean time I installed a new 1,500 watt 24V input. I added 2 T-105s. to my 6. 4 series 24V times 2. I am not concerned about the -550 watts because I am not running big stuff. If I need AC or microwave or water heater the 10kw gen handles that. Just lookin to save some gen wear and fuel when just running TV or fridg. I have a Magiic Chef fridg that uses 134r freon and only take 1.2 amps  My LCD TV 15 58 watts. The surround sound anp and DVD takes 28 watts sub woofer 160 watts Satelite probally 25 watts or so. I figure the most at 3-4 amps total. 120 diveded into 1,500=12.5 amps. About 3 times needed. If you read this far how long should I expect between recharges on average[/i]. Let me hear your experience. Have a blessed day. Charlie
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[Nick Badame Refrig/ACC]

Hello Beatenbo,

I strongly reccomend reading william darden's pages on batteries and charging. you will find it very informative

Good Luck-
Nick Badame

http://www.uuhome.de/william.darden//

[Nick Badame Refrig/ACC]

Beatenbo,

Also try this info from Xantrax on charging times

Nick

http://www.xantrex.com/web/id/54/docserve.asp

[Beatenbo]

Thanks Nick, I saw the pics of the inside of your C3. I have one also, it's my 10th bus and I ame sure liking it. I nedd to get a photo posted. Thanks Charlie  www.beatenbo.com

[Nick Badame Refrig/ACC]

Hay Charlie,

Can't wait to see your C3.

Nick-

[Moof]

Hi there,

Here are some basics that may help.  Ohm's law is pretty simple.  Volts x amps = watts, or watts / volts = amps.  So if I have a 1500 watt hair dryer at 110 volts it will draw 13.6 amps.  If you want to figure out amp hours here is another example

You have a refrigerator that draws 4.5 amps at 110 volts. (ok it's a nice refrigerator)  Now say that you expect the refrigerator to run about 4 hours a day to stay cold your calcualtion would look something like this:

4.5 amps x 110 volts = 495 watts  
495 watts x 4 hours / 12 volts = 165 DC amp hours   (if you are working with 24 volts just substitute the 12 for a 24)

So, when you total all of your amp hours up that should let you know what you need for 24 hours.  Now you have to factor in the real world.  Trace Inverters boast an 85% efficiency.  I think a general 75% efficiency is probably a safer guess.  So now take your total amp hours and divide by .75.  So if you started with 450 amp hours you will need 600 amp hours to get what you need while compensating for a 25% loss through the inverter.

Don't forget your batteries.  You should never run them dead.  50% is a good number to work with here.  So you should have enough batteries to provide 1200 amp hours if you want 450 for 24 hours through an inverter.

When you are looking at your batteries use the amp hour rating, not the cold cranking amps.  You may like the CCA number much better, but it doesn't work that way.

A general guide for battery amperage is:

Group 27          90 amps
Group 31        105 amps
4D                 160 amps
8D                 220 amps
6V Golf Cart    225 amps

The 8D's in AGM are getting about 250 amp hours now.  This is a maintenance free battery that is worth the money.  They also weigh about 165lbs each.  It adds up fast.

The basic formulas I used above are:
      
AC Amps * 120 Volts = Watts      
Watts / 12 volts * 1.1 = Actual DC Amps      
Actual DC Amps * Time = DC Amp Hours   

I double checked my math.  Hope this makes sense.

If anyone sees a mistake please jump in.     

Dave T.

[Moof]

Alright, I found a mistake in my math.  Below is the correct way to calculate DC amp hours.  I forgot to multiply the amps by 1.1.  Sorry about that.

You have a refrigerator that draws 4.5 amps at 110 volts. (ok it's a nice refrigerator)  Now say that you expect the refrigerator to run about 4 hours a day to stay cold your calcualtion would look something like this:

4.5 amps x 110 volts = 495 watts   
495 watts / 12 volts x 1.1 x 4 hours = 181.5 DC amp hours   (if you are working with 24 volts just substitute the 12 for a 24)

[Beatenbo]

Thanks Moof.

[TomC]

Simple-if you have a 120v a/c appliance that takes 1.2 amps, thats 12 amps at 12v.  Figuring on 225 amp hours, that would be 18.75 hours to dead or about 9 hours to 50% charge.  If you double the batteries, you can at least double your hours.  It is interesting that the more batteries you have the slower each battery will discharge.  So three battery banks would work out to 27 hrs worth, but in reality, would be closer to 30 or 32 hours.  Anybody tell me why this happens? (just look on battery charts).  Good Luck, TomC